/etc/libvirt/libvirtd.conf

/etc/libvirt/libvirtd.conf

Logging (journalctl -u libvirtd):

#log_level = 3
#log_outputs="3:syslog:libvirtd"

Default Ubuntu 18.04 LTS file:

cat /etc/libvirt/libvirtd.conf
# Master libvirt daemon configuration file
#
# For further information consult https://libvirt.org/format.html
#
# NOTE: the tests/daemon-conf regression test script requires
# that each "PARAMETER = VALUE" line in this file have the parameter
# name just after a leading "#".

#################################################################
#
# Network connectivity controls
#

# Flag listening for secure TLS connections on the public TCP/IP port.
# NB, must pass the --listen flag to the libvirtd process for this to
# have any effect.
#
# It is necessary to setup a CA and issue server certificates before
# using this capability.
#
# This is enabled by default, uncomment this to disable it
#listen_tls = 0

# Listen for unencrypted TCP connections on the public TCP/IP port.
# NB, must pass the --listen flag to the libvirtd process for this to
# have any effect.
#
# Using the TCP socket requires SASL authentication by default. Only
# SASL mechanisms which support data encryption are allowed. This is
# DIGEST_MD5 and GSSAPI (Kerberos5)
#
# This is disabled by default, uncomment this to enable it.
#listen_tcp = 1



# Override the port for accepting secure TLS connections
# This can be a port number, or service name
#
#tls_port = "16514"

# Override the port for accepting insecure TCP connections
# This can be a port number, or service name
#
#tcp_port = "16509"


# Override the default configuration which binds to all network
# interfaces. This can be a numeric IPv4/6 address, or hostname
#
# If the libvirtd service is started in parallel with network
# startup (e.g. with systemd), binding to addresses other than
# the wildcards (0.0.0.0/::) might not be available yet.
#
#listen_addr = "192.168.0.1"


# Flag toggling mDNS advertizement of the libvirt service.
#
# Alternatively can disable for all services on a host by
# stopping the Avahi daemon
#
# This is disabled by default, uncomment this to enable it
#mdns_adv = 1

# Override the default mDNS advertizement name. This must be
# unique on the immediate broadcast network.
#
# The default is "Virtualization Host HOSTNAME", where HOSTNAME
# is substituted for the short hostname of the machine (without domain)
#
#mdns_name = "Virtualization Host Joe Demo"


#################################################################
#
# UNIX socket access controls
#

# Set the UNIX domain socket group ownership. This can be used to
# allow a 'trusted' set of users access to management capabilities
# without becoming root.
#
# This is restricted to 'root' by default.
unix_sock_group = "libvirt"

# Set the UNIX socket permissions for the R/O socket. This is used
# for monitoring VM status only
#
# Default allows any user. If setting group ownership, you may want to
# restrict this too.
unix_sock_ro_perms = "0777"

# Set the UNIX socket permissions for the R/W socket. This is used
# for full management of VMs
#
# Default allows only root. If PolicyKit is enabled on the socket,
# the default will change to allow everyone (eg, 0777)
#
# If not using PolicyKit and setting group ownership for access
# control, then you may want to relax this too.
unix_sock_rw_perms = "0770"

# Set the UNIX socket permissions for the admin interface socket.
#
# Default allows only owner (root), do not change it unless you are
# sure to whom you are exposing the access to.
#unix_sock_admin_perms = "0700"

# Set the name of the directory in which sockets will be found/created.
#unix_sock_dir = "/var/run/libvirt"



#################################################################
#
# Authentication.
#
#  - none: do not perform auth checks. If you can connect to the
#          socket you are allowed. This is suitable if there are
#          restrictions on connecting to the socket (eg, UNIX
#          socket permissions), or if there is a lower layer in
#          the network providing auth (eg, TLS/x509 certificates)
#
#  - sasl: use SASL infrastructure. The actual auth scheme is then
#          controlled from /etc/sasl2/libvirt.conf. For the TCP
#          socket only GSSAPI & DIGEST-MD5 mechanisms will be used.
#          For non-TCP or TLS sockets, any scheme is allowed.
#
#  - polkit: use PolicyKit to authenticate. This is only suitable
#            for use on the UNIX sockets. The default policy will
#            require a user to supply their own password to gain
#            full read/write access (aka sudo like), while anyone
#            is allowed read/only access.
#
# Set an authentication scheme for UNIX read-only sockets
# By default socket permissions allow anyone to connect
#
# To restrict monitoring of domains you may wish to enable
# an authentication mechanism here
auth_unix_ro = "none"

# Set an authentication scheme for UNIX read-write sockets
# By default socket permissions only allow root. If PolicyKit
# support was compiled into libvirt, the default will be to
# use 'polkit' auth.
#
# If the unix_sock_rw_perms are changed you may wish to enable
# an authentication mechanism here
auth_unix_rw = "none"

# Change the authentication scheme for TCP sockets.
#
# If you don't enable SASL, then all TCP traffic is cleartext.
# Don't do this outside of a dev/test scenario. For real world
# use, always enable SASL and use the GSSAPI or DIGEST-MD5
# mechanism in /etc/sasl2/libvirt.conf
#auth_tcp = "sasl"

# Change the authentication scheme for TLS sockets.
#
# TLS sockets already have encryption provided by the TLS
# layer, and limited authentication is done by certificates
#
# It is possible to make use of any SASL authentication
# mechanism as well, by using 'sasl' for this option
#auth_tls = "none"


# Change the API access control scheme
#
# By default an authenticated user is allowed access
# to all APIs. Access drivers can place restrictions
# on this. By default the 'nop' driver is enabled,
# meaning no access control checks are done once a
# client has authenticated with libvirtd
#
#access_drivers = [ "polkit" ]

#################################################################
#
# TLS x509 certificate configuration
#


# Override the default server key file path
#
#key_file = "/etc/pki/libvirt/private/serverkey.pem"

# Override the default server certificate file path
#
#cert_file = "/etc/pki/libvirt/servercert.pem"

# Override the default CA certificate path
#
#ca_file = "/etc/pki/CA/cacert.pem"

# Specify a certificate revocation list.
#
# Defaults to not using a CRL, uncomment to enable it
#crl_file = "/etc/pki/CA/crl.pem"



#################################################################
#
# Authorization controls
#


# Flag to disable verification of our own server certificates
#
# When libvirtd starts it performs some sanity checks against
# its own certificates.
#
# Default is to always run sanity checks. Uncommenting this
# will disable sanity checks which is not a good idea
#tls_no_sanity_certificate = 1

# Flag to disable verification of client certificates
#
# Client certificate verification is the primary authentication mechanism.
# Any client which does not present a certificate signed by the CA
# will be rejected.
#
# Default is to always verify. Uncommenting this will disable
# verification - make sure an IP whitelist is set
#tls_no_verify_certificate = 1


# A whitelist of allowed x509 Distinguished Names
# This list may contain wildcards such as
#
#    "C=GB,ST=London,L=London,O=Red Hat,CN=*"
#
# See the POSIX fnmatch function for the format of the wildcards.
#
# NB If this is an empty list, no client can connect, so comment out
# entirely rather than using empty list to disable these checks
#
# By default, no DN's are checked
#tls_allowed_dn_list = ["DN1", "DN2"]


# A whitelist of allowed SASL usernames. The format for username
# depends on the SASL authentication mechanism. Kerberos usernames
# look like username@REALM
#
# This list may contain wildcards such as
#
#    "*@EXAMPLE.COM"
#
# See the POSIX fnmatch function for the format of the wildcards.
#
# NB If this is an empty list, no client can connect, so comment out
# entirely rather than using empty list to disable these checks
#
# By default, no Username's are checked
#sasl_allowed_username_list = ["[email protected]", "[email protected]" ]


# Override the compile time default TLS priority string. The
# default is usually "NORMAL" unless overridden at build time.
# Only set this is it is desired for libvirt to deviate from
# the global default settings.
#
#tls_priority="NORMAL"


#################################################################
#
# Processing controls
#

# The maximum number of concurrent client connections to allow
# over all sockets combined.
#max_clients = 5000

# The maximum length of queue of connections waiting to be
# accepted by the daemon. Note, that some protocols supporting
# retransmission may obey this so that a later reattempt at
# connection succeeds.
#max_queued_clients = 1000

# The maximum length of queue of accepted but not yet
# authenticated clients. The default value is 20. Set this to
# zero to turn this feature off.
#max_anonymous_clients = 20

# The minimum limit sets the number of workers to start up
# initially. If the number of active clients exceeds this,
# then more threads are spawned, up to max_workers limit.
# Typically you'd want max_workers to equal maximum number
# of clients allowed
#min_workers = 5
#max_workers = 20


# The number of priority workers. If all workers from above
# pool are stuck, some calls marked as high priority
# (notably domainDestroy) can be executed in this pool.
#prio_workers = 5

# Limit on concurrent requests from a single client
# connection. To avoid one client monopolizing the server
# this should be a small fraction of the global max_workers
# parameter.
#max_client_requests = 5

# Same processing controls, but this time for the admin interface.
# For description of each option, be so kind to scroll few lines
# upwards.

#admin_min_workers = 1
#admin_max_workers = 5
#admin_max_clients = 5
#admin_max_queued_clients = 5
#admin_max_client_requests = 5

#################################################################
#
# Logging controls
#

# Logging level: 4 errors, 3 warnings, 2 information, 1 debug
# basically 1 will log everything possible
# Note: Journald may employ rate limiting of the messages logged
# and thus lock up the libvirt daemon. To use the debug level with
# journald you have to specify it explicitly in 'log_outputs', otherwise
# only information level messages will be logged.
#log_level = 3

# Logging filters:
# A filter allows to select a different logging level for a given category
# of logs
# The format for a filter is one of:
#    x:name
#    x:+name

#      where name is a string which is matched against the category
#      given in the VIR_LOG_INIT() at the top of each libvirt source
#      file, e.g., "remote", "qemu", or "util.json" (the name in the
#      filter can be a substring of the full category name, in order
#      to match multiple similar categories), the optional "+" prefix
#      tells libvirt to log stack trace for each message matching
#      name, and x is the minimal level where matching messages should
#      be logged:

#    1: DEBUG
#    2: INFO
#    3: WARNING
#    4: ERROR
#
# Multiple filters can be defined in a single @filters, they just need to be
# separated by spaces.
#
# e.g. to only get warning or errors from the remote layer and only errors
# from the event layer:
#log_filters="3:remote 4:event"

# Logging outputs:
# An output is one of the places to save logging information
# The format for an output can be:
#    x:stderr
#      output goes to stderr
#    x:syslog:name
#      use syslog for the output and use the given name as the ident
#    x:file:file_path
#      output to a file, with the given filepath
#    x:journald
#      output to journald logging system
# In all case the x prefix is the minimal level, acting as a filter
#    1: DEBUG
#    2: INFO
#    3: WARNING
#    4: ERROR
#
# Multiple outputs can be defined, they just need to be separated by spaces.
# e.g. to log all warnings and errors to syslog under the libvirtd ident:
#log_outputs="3:syslog:libvirtd"
#

# Log debug buffer size:
#
# This configuration option is no longer used, since the global
# log buffer functionality has been removed. Please configure
# suitable log_outputs/log_filters settings to obtain logs.
#log_buffer_size = 64


##################################################################
#
# Auditing
#
# This setting allows usage of the auditing subsystem to be altered:
#
#   audit_level == 0  -> disable all auditing
#   audit_level == 1  -> enable auditing, only if enabled on host (default)
#   audit_level == 2  -> enable auditing, and exit if disabled on host
#
#audit_level = 2
#
# If set to 1, then audit messages will also be sent
# via libvirt logging infrastructure. Defaults to 0
#
#audit_logging = 1

###################################################################
# UUID of the host:
# Host UUID is read from one of the sources specified in host_uuid_source.
#
# - 'smbios': fetch the UUID from 'dmidecode -s system-uuid'
# - 'machine-id': fetch the UUID from /etc/machine-id
#
# The host_uuid_source default is 'smbios'. If 'dmidecode' does not provide
# a valid UUID a temporary UUID will be generated.
#
# Another option is to specify host UUID in host_uuid.
#
# Keep the format of the example UUID below. UUID must not have all digits
# be the same.

# NB This default all-zeros UUID will not work. Replace
# it with the output of the 'uuidgen' command and then
# uncomment this entry
#host_uuid = "00000000-0000-0000-0000-000000000000"
#host_uuid_source = "smbios"

###################################################################
# Keepalive protocol:
# This allows libvirtd to detect broken client connections or even
# dead clients.  A keepalive message is sent to a client after
# keepalive_interval seconds of inactivity to check if the client is
# still responding; keepalive_count is a maximum number of keepalive
# messages that are allowed to be sent to the client without getting
# any response before the connection is considered broken.  In other
# words, the connection is automatically closed approximately after
# keepalive_interval * (keepalive_count + 1) seconds since the last
# message received from the client.  If keepalive_interval is set to
# -1, libvirtd will never send keepalive requests; however clients
# can still send them and the daemon will send responses.  When
# keepalive_count is set to 0, connections will be automatically
# closed after keepalive_interval seconds of inactivity without
# sending any keepalive messages.
#
#keepalive_interval = 5
#keepalive_count = 5

#
# These configuration options are no longer used.  There is no way to
# restrict such clients from connecting since they first need to
# connect in order to ask for keepalive.
#
#keepalive_required = 1
#admin_keepalive_required = 1

# Keepalive settings for the admin interface
#admin_keepalive_interval = 5
#admin_keepalive_count = 5

###################################################################
# Open vSwitch:
# This allows to specify a timeout for openvswitch calls made by
# libvirt. The ovs-vsctl utility is used for the configuration and
# its timeout option is set by default to 5 seconds to avoid
# potential infinite waits blocking libvirt.
#
#ovs_timeout = 5

See also
* libvirt, virtlogd.conf, /etc/libvirt/storage/, libvirt-guests.sh, /etc/libvirt/virtlogd.conf, /var/lib/libvirt/images/
* libvirtd: systemctl status libvirtd, systemctl status libvirt-guests, Libvirt release notes, logs, libvirtd.conf, /etc/libvirt/, /var/log/libvirt/